Assessing the bleaching capacity of some Cameroonian clays on vegetable oils

Abstract

Four Cameroonian clays, constituted mainly of smectites associated to minor amounts of kaolinite and quartz, have been used to bleach palm oil, cottonseed oil and maize germ oil. Kinetic studies show that the best temperature and contact time for optimum bleaching of vegetable oil varied with the type of oil; these are: 95 °C and 2.5 h for palm oil, 85 °C and 0.25 h for cottonseed oil, and 85 °C and 0.5 h for maize germ oil. The bleaching ability of natural clays was poor when compared with that of industrial adsorbents. Acid activation of Cameroonian clays with 1N sulphuric acid solution increased tremendously their adsorptive capacity, which therefore matches those of the industrial adsorbents. Further increase of the concentration of the acid solution used for clay activation did not induce a noticeable increase in the bleaching power of the adsorbents. This was attributed to the fact that the increase in the surface area is due to the formation of silica but the surface area of H-clays remains almost constant over strong acid leaching and silica has very poor bleaching power of vegetable oils. FT-IR spectroscopy studies of the adsorbents after bleaching suggest strong interactions between the clays and adsorbent surface. Acid and iodine values of bleached oils reveal that oils are not deteriorated by clays during the bleaching process. The overall results lead to the conclusion that Cameroonian clays can be converted into potent adsorbents for bleaching vegetable oils.