Factors influencing vegetable oil bleaching by adsorption

Abstract

Vegetable oil bleaching by adsorption involves the removal of color particles which are either dissolved or colloidally dispersed in the oil. This type of adsorption follows an exponential relationship and the Freundlich equation was utilized in correlating the data. In utilizing this equation, the color of the oil was assumed proportional to the concentration of the color particles, and a color measurement system based on the Beer‐Lambert Law was devised. This system involves a measurement of the transmittance of light of 475 millimicrons wave length through the oil. A Coleman, Model 11, Spectrophotometer was used for the transmittance measurements. Spectral transmittance curves for cottonseed and soybean oil, bleached and unbleached, are given. The effect of the variables of temperature, time of contact, and particle size on the activity of several adsorbents was determined. It was found that the activity of each adsorbent is at a maximum at some particular temperature. The adsorbents were grouped into three general classes: acid‐activated clays, natural earths, and materials high in silica content, and it was found that adsorbents in the same class have a temperature of maximum activity within the same range. The effectiveness of 16 different adsorbents in bleaching a refined cottonseed oil was determined by utilizing the Freundlich equation and plotting adsorption isotherms for each adsorbent. Similar data are given for 10 different adsorbents in bleaching a refined soybean oil. On the basis of adsorbent activity, acid‐activated clays were 11/s to 2 times as effective as natural earths.

Soy oil lutein adsorption by rice hull ash

“…The data in Figures 1 and 2 suggest that the pigment binding abilities of acid ash and acid activated clay were similar. The increase in ash activity after acid activation parallels similar findings in conventional bleaching clays (5). Acid activation of montmorillonite opens up the crystal structure to produce a greater surface area available for adsorption.…”

Adsorption of Gossypol from Cottonseed Oil on Oxides

“…Other workers have either assumed or suggested that adsorption of pigments, mainly gossypol and its derivatives, from cottonseed oil follows the Freundlich isotherm (12,14). Those studies involved pigment mixtures and not a pure substance as in the present case.…”

“…• C (12,13,18,19). There are discrepancies about the respective influence of the SiO 2 and Al 2 O 3 contents of adsorbents and their efficiency (14,15,18,19).…”

“…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).…”

“…A number of studies have been carried out on the removal of pigments from cottonseed oil by adsorption (12)(13)(14)(15)(16)(17)(18)(19)(20)(21). The results obtained are hardly comparable since the experimental conditions are different from each other and the examined systems are often complex.…”