Elucidating how two different types of bleaching earths widely used in vegetable oils industry remove carotenes from palm oil: equilibrium, kinetics and thermodynamic parameters

Abstract

This work compared the mechanisms of adsorption of carotenes from hybrid palm oil onto two kinds of bleaching earths widely used by industrial refiners (acid-activated and neutral). First, it was performed a deep characterization of adsorbent surfaces: acid activated adsorbent showed micropore volumes twice larger than the neutral. FTIR analysis of adsorbent after adsorption demonstrated that active site was Si–O–Si for both adsorbents. However, comparison of peak shapes suggested distinctive interactions between adsorbent/adsorbate for each adsorbent. Latterly, an extensive kinetic and equilibrium study was performed. Kinetic data were in accordance with pseudo-first and pseudo-second-order models. Adjusting to the intra-particle diffusion model evidenced more than one mechanism controlling the adsorption process. Equilibrium data demonstrated adsorption is only favorable at low carotene concentration at liquid phase for acid adsorbent (lower than 1 mg/mL). For neutral adsorbent, it was not clearly observed a favorable region with the studied conditions. The acid adsorbent could adsorb more carotenes per adsorbent weight than neutral. Finally, neutral adsorbent showed higher heterogeneity of interaction between adsorbate and adsorbent than the acid, especially at low adsorbent coverages.