Adsorption isotherms of pigments from alkali-refined vegetable oils with clay minerals |
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Authors: | Keito Boki Moriaki Kubo Naohito Kawasaki Hidehito Mori |
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Affiliation: | (1) Faculty of Pharmaceutical Sciences, Kinki University, Kowakae, 3-4-1, Higashi-Osaka, 577 Osaka, Japan |
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Abstract: | Adsorption isotherms of pigments from alkali-refined oils (rapeseed, soybean, wheatgerm, safflower, corn, cottonseed and sunflower)
were measured to investigate the applicability of the Langmuir and Freundlich equations and to elucidate the adsorption characteristics
of pigments on sepiolites and standard activated clay. The Freundlich equation was more applicable to the experimental adsorption
isotherms. The equilibrium amount adsorbed, acidity, pore size distribution and inflection of the Freundlich isotherms could
be explained by assuming that pigments were adsorbed on the stronger acid sites in smaller pores at low concentration, and
then in the larger ones when the concentration increased. The amount adsorbed increased with a rise in adsorption temperatures
from 70 to 110°C, and the heat of adsorption was below 10 kcal/mol. The results indicate that pigments were physically adsorbed
on the acid sites activated at higher adsorption temperatures. |
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Keywords: | Adsorption isotherm alkali-refined oil clay Freundlich equation heat of adsorption physical adsorption pigments |
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