Equilibrium, Thermodynamic and Kinetic Studies of Palm Oil -carotene Adsorption by Composites Based Silica-Smectite

Three silica-smectite based composites with different structures denoted CSS1, CSS2 and CSS3 were used to adsorb palm oil beta-carotene via batch tests. The optimal conditions were 2% (w/w), 40 min and 95 degrees C for adsorbent dosage, contact time, and temperature respectively. The bleaching capacity was found to be 64% for CSS1, 79% for CSS2 and 92% for CSS3. R-2 and Root Mean Square Deviation values indicated that equilibrium data were described well by Freundlich isotherm while the second-order and intraparticle diffusion fitted well the kinetic data, The activation energy values were less than 10 kJ/mol for all adsorbents and the enthalpy change ranged from 13.8 to 23.0 kJ/mol, pointing to a physical adsorption and an endothermic process. In addition, as the temperature increased, from 60 to 95 degrees C, the Gibbs free energy Delta G decreased, (- 964.20 to - 2441.30 J/mol for CSS1), (- 1717.50 to - 7175.90 J/mol for CSS2) and (- 2510.30 to - 3476.90 J/mol for CSS3) revealing the spontaneous character of the process at higher temperature. The positive values of entropy change (57.5 <=Delta S <= 87.6 J/mol.K) Delta S suggested an increase in the randomness at the adsorbent-palm oil interface, related to the redistribution of energy between the beta-carotene molecules and the adsorbent. Each of the three composites behaved as a good adsorbent, but CSS3 outperformed CSS2 and CSS1.