Influence of chemical composition of activated calcium bentonites and sodium bentonites on palm oil bleaching capacity and oil quality
2022
Dhurakit, P. | Dolphen, R. | Thiravetyan, P.
The efficiency of clays in bleaching degummed palm oil depends on their unique characteristics. This study sheds new light on a novel characteristic which impacts on the quality and bleaching capacity of activated clay. Although bentonites may originate from different areas, their structural modifications can make them ideally suited for bleaching. Calcium (Ca)-bentonites and sodium (Na)-bentonites, including activated forms of both clays, were investigated in depth. Interestingly, X-ray fluorescence (XRF) spectrometry indicated that the high bleaching capacity of Na-bentonite was correlated with silica (SiO₂) and alumina (Al₂ O₃) contents in the range of 68.90%-85.20% and 8.96%-16.60% by weight (wt), respectively. The results showed that Na-bentonite treated with 1.5 M sulphuric acid (H₂ SO₄) at a clay: acid ratio of 10:50 (w v–1) and refluxing time of 8 hr had a higher bleaching capacity (78.04%) than commercial clay (67.09%). These characteristics can provide a suitable reaction space at the interlayer for adsorption of pigments and impurities. Moreover, the specific surface area and total pore volume of this activated clay also increased. After bleaching by treated Na-bentonite with 1.5 M H₂SO₄, degummed palm oil appeared to be of good quality, leading to less deterioration and rancidity due to decreased free fatty acid (FFA), unsaturated fatty acid, iron (Fe) and phosphorus (P) contents.
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