Characteristics and Efficiency of Bleaching Clays in the Physical Refining of Palm Oil

The physicochemical properties of the bleaching clays used in the physical refining of palm oil were characterized. The clays evaluated were acid-activated clays (Taiko Supreme 1B, Taiko PGEO and SBE Gold), mixed clays (Pure Flo) and natural clays (attapulgites like A4 and HRL 200). Electron micrographs of attapulgites displayed a spread of needle like lath on the surface while the acid activated clays mostly showed irregular flakes on the surface. The analysis of Freundlich isotherm was found to be more applicable than Langmuir isotherm in the adsorption isotherm data of pigments, carotene and chlorophyll on various types of bleaching clays. However, the adsorption of trace iron on the clays fitted the Langmuir model better than the Freundlich model. The results suggested that the high surface area in the acid-activated did not necessary possess better bleaching efficiency than other clays. Pure Flo, a neutral clay, is the best bleaching clay for adsorbing chlorophyll compared with other clays. This is contrary to the general belief that acid-activated clays is better in adsorbing chlorophyll. Crude palm oil of poor quality was degummed, bleached and deodorized to evaluate the effectiveness of various bleaching clays using different dosages of 0.8% and 1.5%. The attapulgites are good in adsorbing chlorophyll but not good in adsorbing carotene. An attapulgite clay was heat-activated using different temperatures. The treated samples were tested in order to verify their capacity to bleach palm oil and were compared to the standard commercial bleaching clay. The mildly heat-treated attapulgite was superior to the other clays in adsorbing chlorophyll. The stepwise bleaching process and the single-step bleaching process was also compared between the acid-activated clay, attapulgite and silica. Silica was able to retain more carotene in both processes compared with the other two clays. However, the acid-activated clay was found to adsorb iron better in the stepwise process.

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