Surface Active Sites and Textural Features of Bleaching Clays

Abstract

Vegetable oil refining process involves a bleaching stage wherein clay mineral is commonly used to promote “bleaching” or removal of contaminants from oil treated at higher temperature and under vacuum. Clay minerals have unique properties including high surface area, porosity, and presence of surface active sites. These important features help the mineral promote adsorption and catalysis of organic contaminants/pigments during bleaching of vegetable oils. Essentially, the process of bleaching is aimed at removing contaminants and undesired components from raw oils to preserve taste and impart quality to the oil. As such, clays have been extensively used in bleaching of vegetable oils and fats. The performance of natural clay mineral is dependent on their physical and chemical processing including steps like grinding, screening, acid activation, pillaring, thermal processing, and addition of functional active ingredients. Bleaching efficacy is also dependent on oil processing variables (including time, temperature, atmosphere, humidity, and agitation) maintained during bleaching process. To this end, classical and mild acid activation and addition of functional additives are the most commonly applied methods in the oil and fats industry. This article will briefly review the nature of active sites and textural properties impacting the robustness of natural and modified bleaching clays.