Adsorption isotherms of pigments from alkali‐refined vegetable oils with clay minerals

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 ll0°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.

Assessment of the surface areas of silica and clay in acid-leached clay materials using concepts of adsorption on heterogeneous surfaces

“…The differences in Si/Al ratios can probably be related to the initial composition of the clay samples. As determined by Tkac et al [12] by 27 Al MAS NMR, tetrahedral aluminum can be fixed in the silica framework and remain stable against further acid attack.…”

Adsorption of Gossypol from Cottonseed Oil on Oxides

“…Reports on the adsorptive removal of coloring from oil and other solutions often claim that the Freundlich equation is applicable (12,14,20,(28)(29)(30). A fit of the Langmuir equation has been reported for adsorption of β-carotene from organic solvents by activated earth and acid-activated montmorillonites (32)(33)(34)(35).…”

“…Acid activation of clay generally leads to an improvement of bleaching capacity (17,18,21). However, few authors (17)(18)(19)(20) characterized the texture of the adsorbents; Zaki et al (18) found that the bleaching capacity of activated natural clays varied with pore size and an optimum was observed at a pore diameter of 10 to 12 nm.…”

Decolorization of vegetable oils: Chlorophyll-a adsorption by acid-activated sepiolite

“…The adsorption of pigment from vegetable oils with various types of adsorbent has been extensively investigated, and many studies involve the adsorption isotherms of coloring materials, such as chlorophyll-a [2][3][4][5][6][7][8][9][10][11][12][13][14][15]. However, no study to date has been done on the adsorption of chlorophyll-a onto sepiolite.…”