| The role of edible oils in human health, along with the development of the edible oils industry and improvement of human being's living standards, has gained increasing attention. Hence, the investigation of oil processing procedures are of rising importance for oil quality control.. Bleaching is one of the crucial steps in oil refining. Elucidation of the oil bleaching procedure with respect to its mechanism of action and influence on oil quality have, therefore, paramount value in maintaining oil flavor and nutrition, understanding the effects of oil processing technology and adsorbents on oil quality, guaranteeing human health, and upgrading oil processing technolgy.An extensive study was performed on the mineral characteristics and modification mechanism of attapulgite in terms of thermal properties (DSC-TGA), chemical composition (FT-IR spectroscopy), morphology (SEM), specific surface area (BET method), pore size distribution (gas adsorption method), basal spacing (XRD), elemental composition (XPS), and acidic points distribution (NH3-TPD method). The mechanism of attapulgite modification in preparing oil bleaching agents was first established to be a low acidic process with the following major changes involved: acid treatment induced deaggregation of the fasciculi,and partial substitution of the cation in the octahedral crystal structure, and medium temperature activation enhanced exposure of broken bonds. Acid treatment and medium temperature activation, therefore, constitute the predominant factors in modifying the structure of attapulgite.,The crystal structure of attapulgite was not changed, but it became more ordered; the conversion and re-crystalization of hydration decomposed transitional products of montmorillonite was stimulated; and the surface characteristics and pore structure of attaplgite was remarkable affected.Oil bleaching tests showed an adsorption curve fittable to the Freundlich isotherm. The calculated thermodynamic parameters (â–³G,â–³H,â–³S) indicated that the the oil bleaching process was exothermic. The adsorption was a physical process composed of pore filling, Van der Waals'forces and H-bonding forces. The adsorption capacity was closely related to the dioctahedral crystal structure of the attapulgite, large amounts of nanoscale channels, and surface modification formed acidic sites, The changes in the channel structure played a key role in improving the oil bleaching performance of the modified attapulgite. The Bangham equation for nonhomogeneous surface absorption systems was used to compare the adsorption kinetics of single- and multi- sorbate on attapulgite using unitless variables. Oil bleaching with attapulgite was shown to be a competetive adsorption process consisting of two steps: one of rapid mass tranfer, diffusion and adsorption followed by the other of relatively slower adsorption. The adsorption rate of the components in the oil bleaching system followed the sequence: chlorophyll > carotinoids>free fatty acids (FFAs) > phospholipids. Analyses of the adsorption process by FT-IR and SPME-GC-MS indicated that the modified attapulgite has remarkable catalytic activities towards a series of reactions including hydrolysis of triglycerides, decomposition of hydrogen peroxides, and oxidization, isomerization and polymerization of fatty acids.Analyses of the adsorption process by FT-IR and SPME-GC-MS indicated that the modified attapulgite has unremarkable catalytic activities towards primary oxidative reactions, and has adsorptive activity stronger than catalytic activity towards hydrogen peroxide. Acidic sites on the surface of attapulgite has significant catalytic activity towards the formation of polar compounds, especially furanoids, but has unremarkable catalytic activities towards the formation of other substances. The isomerization of fatty acids was caused by the heating and attapulgite combined, with the former playing a key role in producing trans fatty acids and the latter in providing catalytic activity.
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