The role of bleaching clays and synthetic silica in palm oil physical refining

The adsorption characteristics of three bleaching clays having different degrees of activation were studied in a palm oil physical refining process. Different clay types and concentrations were used in combination with a fixed amount of synthetic silica. The analytical characteristics of crude, degummed, bleached and steam-refined oils were compared. The isotherms of colour removal vs. clay concentration demonstrated that acid-activated clays were more efficient than natural clay in removing carotene pigments. The phosphorus adsorption capacity of clay seemed also to be positively affected by acid activation. However, no relationship was observed between acid activation and copper, lead or iron adsorption; the adsorption of these metal ions seemed more probably related to the presence of synthetic silica in the bleaching mixes. Although the tested clays had different activities, the analytical characteristics of the corresponding refined palm oil samples were similar. This can be explained by the fact that synthetic silica, due to its synergic action with clays, smoothes the differences between the performances of the various clays.