Clays used with activated carbon

Activated clays and fuller s earth are used extensively for decolorizing fats and oils—animal, vegetable, and mineral. In a number of applications, they are used alone but for some fats and oils an admixture with activated carbon is required in order to attain a desired decolorization. Moreover, carbon will remove off-odors and tastes, whereas clays frequently impart a so-called earthy flavor and odor. Consequently, even when not needed for removal of color carbon is often admixed with clay to ensure freedom from any earthy flavor. 

Composition. Among the most commonly used support materials are aluminas, siUcas, and aluminosihcates with a wide range of alumina to sihca ratios, as well as activated carbon, siUcon carbide, selected clays, various ceramics, artificial and natural 2eohtes, kieselguhr, and pumice. Polymeric... 

The raw material has to be washed to remove impurities. Diluted sodium hydroxide allows the removal of phenols and benzonitrile, and diluted sulphuric acid reacts with pyridine bases. The resulting material is distilled to concentrate the unsaturated compounds (raw feedstock for coumarone-indene resin production), and separate and recover interesting non-polymerizable compounds (naphthalene, benzene, toluene, xylenes). Once the unsaturated compounds are distilled, they are treated with small amounts of sulphuric acid to improve their colour activated carbons or clays can be also used. The resulting material is subjected to polymerization. It is important to avoid long storage time of the feedstock because oxidation processes can easily occur, affecting the polymerization reaction and the colour of the coumarone-indene resins. 

The dispersion and solid-state ion exchange of ZnCl2 on to the surface of NaY zeolite by use of microwave irradiation [17] and modification of the surface of active carbon as catalyst support by means of microwave induced treatment have also been reported [18]. The ion-exchange reactions of both cationic (montmorillonites) and anionic clays (layered double hydroxides) were greatly accelerated under conditions of microwave heating compared with other techniques currently available [19.]... 

Besides using the bioactive agent to detect the ion of interest, another approach can include monitoring an ion by its inhibitory effect upon enzymatic activity. For example, horseradish peroxidase (HRP) can be immobilised onto one gate of a REFET [107] allowing the presence of cyanide ion to be measured at concentrations of 10 3-10 7 M. The approach used here is to monitor the inhibition of the enzymatic HRP effect, by the cyanide ion, on ascorbic acid. Even lower levels (10 10 M) of detection can be obtained using a polyphenol oxidase/clay composite immobilised on carbon, with no interference from chloride, nitrate or bromide [108]. 

It is a mass transfer between a mobile, solid, or liquid phase, and the adsorption bed packed in a reactor. To carry out adsorption, a reactor, where a dynamic adsorption process will occur, is packed with an adsorbent [2], The adsorbents normally used for these applications are active carbons, zeolites and related materials, silica, mesoporous molecular sieves, alumina, titanium dioxide, magnesium oxide, clays, and pillared clays. 

Similarly, there is a great potential in the use of water vapour for the analysis of the porous texture, because it has considerable potential due to both the easy experimental conditions (at room temperature the whole range of relative pressures can be covered) and the characteristics of the molecule itself (polar molecule and small kinetic diameter-0.28 nm). This vapour is widely used in the characterisation of inorganic porous solids, such as zeolites, silicas, and clays. However, its interaction with carbon materials (microporous carbons coals, activated carbon fibres, carbon molecular sieves and porous carbons activated carbons), is more complex than the interaction of non-polar molecules [8]. 

The Langmuir equation has been used to describe adsorption of p carotene from solution onto activated bleaching clays (8) and free fatty acid from isooctane solution by acid-washed rice hull ash (9). Likewise, isotherm analysis of the commercial bleaching of rubber and melon seed oil by Fullers earth, activated carbon, and Fullers earth/activated carbon mixture (10) followed Langmuir behavior at 55°C and 80°C, suggesting the possibility of monolayer adsorption with little competition. This behavior was not observed at 30°C where the isotherm no longer applies, because of desorption. The amount of adsorbent was kept constant while varying... 

As with powdered activated carbon, amorphous silica hydrogels are used in conjunction with bleaching clays in the adsorptive purification of fats and oils. Silica hydrogels possessing average pore diameters greater than about 60 A exhibit high... 

Adsorptive purihcation, in its most general sense, involves the use of adsorbents to remove undesirable constiments and contaminants from fats and oils by adsorptive mechanisms. It must be noted, however, that although different adsorbents do exhibit some degree of selectivity for certain adsorbates (see Section 4.3), none exhibit specific selectivity for a single compound or chemical. Some trace constituents that are desirable (e.g., tocopherols) will also be removed. According to Boki et al. (106), 20-40% of the tocopherols present in most alkali-refined oils are removed by bleaching with acid-activated bleaching clay the exception is soybean oil, which only loses 3-5% (71, 105). Buxton has reported (107) that activated carbon removes antioxidants from fish hver oils and renders the vitamin A in the oil unstable. 

An advantage of most synthetic sorbents over activated carbon is the better regeneration ability, for which hot steam is usually used. With the appHca-tion of these procedures in remediation projects, a good infrastructure and supplying logistics (electricity, hot steam) are clearly an advantage. Since the sorbents materials react sensitively to fine parficles (e.g. clay, fine silt), iron and manganese, the possible occurrence of these substances should be clarified before hand. 

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