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Decolorization of vegetable oils: A study of the mechanism of adsorption of b-carotene by an acid-activated bentonite from Cyprus

Christidis Georgios, Sotiria Kosiari

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Summary

The mechanism of decolorization of crude maize and sunflower oils was studied by means ofadsorption of b-carotene by a low-grade bentonite , containin g mixed-layered illite-smectite.Decolorization depends on temperature and the time required for equilibrium decreases with increasingtemperature. The study of the kinetics of adsorption showed that decolorization of maize oil is a first-orderprocess which occurs in two steps: a first fast step with higher activation energy (25.6 kJ mol –1),indicating the influence of a chemical interaction between the pigment and the clay surface, followed by asecond slow step with low activation energy (12.3 kJ mol –1), characteristic of physical adsorption on thepreviously adsorbed molecules. Decolorization of sunflower oil is also a first-order process, described by asingle mechanism with intermediate activation energy (19.0 kJ mol –1). Adsorption isotherms ofdecolorization of maize oil follow the Freundlich equation, indicating the existence of heterogeneousadsorption sites on the solid’s surface. Heterogeneity is attributed both to different active centers on thesmectite surface (Bro¨ nsted and Lewis centers) and to the different phases present in bentonite, such asillitic layers and clinoptilolite, which also have active centers on their surfaces.

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