Bleaching earth

Filter aids may be applied in one of two ways. The first method involves the use of a precoat filter aid, which can be applied as a thin layer over the filter before the suspension is pumped to the apparatus. A precoat prevents fine suspension particles from becoming so entangled in the filter medium that its resistance becomes exces-sive. In addition it facilitates the removal of filter cake at the end of the filtration cycle. The second application method involves incorporation of a certain amount of the material with the suspension before introducing it to the filter. The addition of filter aids increases the porosity of the sludge, decreases its compressibility, and reduces the resistance of the cake. In some cases the filter aid displays an adsorption action, which results in particle separation of sizes down to 0.1 /i. The adsorption ability of certain filter aids, such as bleached earth and activated charcoals, is manifest by a decoloring of the suspension s liquid phase. This practice is widely used for treating fats and oils. The properties of these additives are determined by the characteristics... 

Florida-bleicherde, -erde, /. Florida (bleaching) earth. 

Acid orange 51 (acid dye) Activated 8.45 bleaching earth (clay) 0.0552 Tsai et al. (2004)... 

M. Mahramanlioglu, I. Kizilcikli, I.O. Biccer, Adsorption of fluoride from aqueous solution by acid treated spent bleaching earth, J. Fluorine Chem. 115 (1) (2002) 41-47. 

Colour. The colour of fully-refined oils is less intense than non-refined oils. Acid and alkaline treatment, and the use of bleaching earths, would all be expected to affect the colour of the oil. The method used could be spectrophotometric or colorimetric. 

In 1974, Homberg (1974) reported that the action of bleaching earth on cholesterol in solutions of both synthetic triacylglycerol (TAG) and hexane caused the formation of the dehydration product cholesta-3,5-diene. Subsequently it was reported that bleaching of butterfat resulted in the formation of cholesta-3,5-diene (Roderbourg and Kuzdzal-Savoie, 1979) and the authors proposed that the detection of this artefact could be used to identify refined butterfat. In a review article (Kochhar, 1983), it was reported that several other authors had identified steradienes in bleached vegetable oils and proposed that the detection of these could be used to identify refined oils or mixtures of refined and unrefined oil. 

In olive oil, the main sterol is (l-sitosterol and this dehydrates to a mixture of 2,4- and 3,5-stigmastadienes on heating to high temperatures or in the presence of a bleaching earth (Grob and Bronz, 1994 Cert and Moreda, 1998). 

The energy of activation for sitosterol dehydration was calculated as 191.0 9.0 kJ/mol, but this is reduced to 70.8-80.6 kJ/mol in the presence of bleaching earths (Gordon and Firman, 2001). The rate of dehydration of other sterols is expected to be similar to that of sitosterol. 

Kojima, S., Du, D., Sato, M., and Park, E. Y. 2004. Efficient production of fatty acid methyl ester from waste activated bleaching earth using diesel oil as organic solvent,... 

The oil is loaded into the reactor, shown with both an agitator and a pumped circulation-spray loop, and heated under vacuum (110-130°C) to reduce water and peroxide contents. Next, the oil is cooled to 70-90°C and the catalyst is added as dry powder at 0.05-0.15 percent or suspended in dry oil. Randomization requires about 30 min, with an additional 15-30 min allowed for completioa After the reaction is complete, the batch is transferred to a postbleacher where the process is arrested by inactivating the catalyst by addition of water or an (phosphoric or citric) acid solution. Bleaching earth, added to absorb the inactivated catalyst and soaps removed by filtration and the oil sent to blending or deodor-ization. Losses from the formation of FFA and FAME are —10 times the catalyst weight, with... 

Active Oxygen Method for Fat Stability (AOM) (Cd 12-57) determines the time (in hours) for a sample of fat or oil to attain a predetermined peroxide value (PV) under the conditions of the test. The method is used to estimate the comparative oxidative stability of fats and oils. The method has been placed in surplus, in favor of Cd 12b-92 (Oil Stability Index), but retains official status and is still used in domestic industry. p-Anisidine Value (AV) (Cd 18-90) determines the amount of aldehydes (principally 2-alkenals and 2,4-dienals) in animal and vegetable fats and oils. These are degradation products of peroxides, which are not removed by bleaching. Some fats and oils chemists propose increased use of this method in purchase specifications. Bleaching Test for Soybean Oil (Cc 8e-s63) determines the color of a sample of soybean oil after treatment with a specified bleaching earth. Specific methods exist for other oil species. 

Other methods employed to refine natural oils involve the use of ion-exchange resins135 and bleached earths.136 Hydrogen peroxide is, however, employed to regenerate these materials for further use. 

The total surface concentration and intensity distribution of acidic and basic active sites are presented in Fig. 7.10. The total height of the stacked bars represents the total surface concentration of the acidic and basic active sites in millimoles per gram. The individual parts of the stacked bar correspond to the intensity distribution. As shown in Fig. 7.10, these data indicate that magnesium silicate has a total acidic and basic site concentration of 1.8 and 2.3 mM/g, respectively [17]. In comparison with other types of adsorbents used in frying oil (activated carbon, alumna [basic], alumina [neutral], alumina [acidic], bleaching earth, dia-tomaceous earth, and silica), magnesium silicate shows the highest values of total acidic and basic sites. 

FIGURE 7.10 Surface concentrations and their intensity distributions for (A) the acidic and (B) the basic sites of adsorbents used in frying oil. A, activated carbon B, alumina (basic) C, alumina (neutral) D, alumina (acidic) E, bleaching earth F, diatomaceous earth G, silica and H, magnesium silicate. 

The configuration of the double bond in naturally occurring fatty acids, present in oils and fats, is predominantly in the cis form. Isomerization can occur if oils and fats are heated at temperatures above 100°C in the presence of bleaching earths or catalysts such as nickel, selenium, sulfur, or iodine. 

Bleaching. The refined oils are usually dark in color owing to the presence of some pigmented materials such as chlorophyll or carotenoids and minor impurities like residual phosphatides, soaps, metals, and oxi-datin products. Bleaching reduces the color by absorbing these colorants on bleaching earth (bentonite clays), or activated charcoal, or both. In addition to decolorization, bleaching clay also absorbs suspended matter and other minor impurities. 

Several bleaching processes have been developed over the years to limit the consumption of bleaching earth. Figure 4.7 shows the flow sheet of a double-batch bleaching process. This is by far the oldest bleaching method, still in use in many refining plants [4]. 

In order to reduce bleaching earth consumption, alternative new multistep bleaching processes have been developed. Figure 4.8 shows the flow sheet of a two-stage counter-current bleaching with a prefiltration process. The main function of prefiltration is to remove all solid impurities as well as to adsorb most of the phosphatides and soaps. This increases bleaching efficiency in the second stage [4]. 

Treatment of lard with bleaching earth decomposes the peroxides and increases the content of conjugated trienes, which absorb at 268 nm. This characteristic has been the basis of a quality control procedure for determining whether lard has been bleached (66). 

During oil processing, chlorophyll completely decomposes to derivatives, which are more difficult to remove during bleaching. This necessitates much higher amounts of activated bleaching earth to be used to achieve complete removal of all chlorophyll derivatives (45). 

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