Acid-activated clay

Adsorbents. Acid activated clays have been widely used to treat mineral, vegetable, and animal oils. The primary objective of such treatment is decolorization and, at least in the case of edible oil, to remove components that contribute to off-tastes. Typically the oil is filtered through a granular clay product or treated with finely ground clay and subsequendy filtered. 

Vaccari (1983,1999) has given a state-of-the-art account of the preparation and catalytic properties of cationic and anionic clays. Some examples of industrial importance have also been reported. Clays exhibit many desirable features, such as low cost, wide range of preparation variables, ease of set-up and wOrk-up, high selectivity, and environmental friendliness. Cationic clays are widespread in nature, whereas anionic clays are rarely found in nature, but they can be synthesized cheaply. Cationic clays are prepared from the minerals but industrial anionic clays are generally synthetic. Smectite clays exhibit both Brpnsted and Lewis acid sites on the edges of the crystals. Hammet s acidity function values are as follows Na -montmorillonite (M), -3 to t- 1.5 NH4VM -3 to 1.5 H M -8.2 to -5.6 acid activated clay less than -8.2. Laporte also has a synthetic version of cationic clays, Laponite. The acid... 

The alkylation is achieved using an acid activated clay catalyst (73). The reaction is performed in nitrogen atmosphere. Namely, nitrogen gas atmosphere or other inert gas atmospheres, in contrast to air gas atmosphere, suppress the formation of products that deactivate the clay catalyst. 

A clay slurry was prepared by adding the Na-exchanged clay to the 15% H2SO4 solution and was refluxed for 3 h. Then the solid in the slurry was separated, washed with the distilled water till the PH of the filtrate reaches 3 to 4. Finally the filtrated cake was dried at 110°C for lOh. The resulting product is atlapulgite (acid-activated clay). 

C. Breen, M. Last Philip, S. Taylor and P. Komadel, Synergic chemical analysis - the coupling of TG with FTIR, MS and GC-MS 2. Catalytic transformation of the gases evolved during the thermal decomposition of HDPE using acid-activated clays, Thermochimica Acta, 363, 93-104 (2000). 

Recently, silica-based synthetic materials have been used in bleaching. The natural bleaching earth, fuller s earth, a hydrated aluminum silicate, mostly has been replaced by acid activated clays, which are sulfuric- or hydrochloric-acid-treated bentonites or montmorillonites. Manufacmrers continuously improve the quality and develop new bleaching earths to meet the market s needs. Higher activity and filterability are the main focuses of such development. 

Palm oil and coconut oil are refined by the physical refining method. The crude oil is bleached with acid-activated clay and citric acid at elevated temperamres under vacuum. The objective is to remove phosphorus (phospholipids), trace metals, oil decomposition products, and some of the color bodies from the crude oil. The volatile impurities in the bleached oil are then removed via steam distillation under very low absolute pressure and high temperature in a deodorizer. 

Oils that have been citric acid conditioned and bleached with non acid-activated clays. 

H30 per liter, but for a solid acid such as acid-activated clay a sharp distinction must be made between soluble acidity and local acid strength . The soluble acidity can be readily measured by convential techniques such as titration or gas volumeter analysis. As to titration, the clay can be dispersed in water, and any acidity thus liberated can be neutralized. On this basis, Thomas, Hickey, and Stecker [89] found that raw montmorillonite yielded 0.41 milliequivalents of acid per gram of dry clay, while after acid treatment (removal of half of the aluminum) this value rose to only 1 milliequivalent per gram. If the clay were a liquid with the density of water, these results would mean hydrogen ion concentrations of 0.41 x 10 and 1 X 10 mole per liter, which corresponds to pH values of 6.39 and 6.00, respectively. Thus, even for the acid-activated clay the soluble acidity is extremely small, and cannot possibly explain the proven catalytic effect of this material. It does, however, explain the fact that TONSIL can be swallowed without harm. 

Against this background, any meaningful characterization of the catalytic activity of acid-activated clay imposes the following conditions ... 

Using a series of indicators with pK values in the range between +3.3 and +0.42, Walling was able to show that acid-activated clays have local acid activities greater than what is found in a solution with a pH = 0.1. 

Acylation of 2-methoxynaphthalene with acetic anhydride was carried out using different solid acid catalysts such as zeolites, acid activated clays, ion exchange resins and sulphated zirconia. The products of the reaction are precursors of many organic and pharmaceutical intermediates. For example, the para isomer of the reaction product, 6-methoxy-2-naphthalene-a-methyl ketone is useful as a raw material for the manufacture of well-known anti-inflammatory dru called naproxen. The reaction products were isolated and confirmed by their melting points, H-NMR, gas chromatography, etc. 

In our earlier experiments we have found that montmorillonite KIO, a commercial acid activated clay is a good catalyst for aniline alkylation [9,10]. This has prompted us to study the effect of acid activation of clay on the reaction. 

Methyl terf-butyl ether (MTBE) is an important industrial product used as oxygenate additive in reformulated gasoline. Environmental concern makes its future uncertain, however. Although mainly manufactured by reaction of isobutylene with methanol, it is also produced commercially from methanol and fcrr-butyl alcohol, a by-product of propylene oxide manufacture. Numerous observations from the use of heteropoly acids have been reported. These compounds were used either as neat acids [74], or supported on oxides [75], silica or K-10 montmorillonite [76]. They were also used in silica-included form [77] and as acidic cesium salts [74,77]. Other catalysts studied were sulfated ZrOj [76], Amberlyst 15 ion-exchange resin [76], HZSM-5 [76], HF-treated montmorillonite, and commercial mineral acid-activated clays [75]. Hydrogen fluoride-treatment of montmorillonite has been shown to furnish particularly active and stable acid sites thereby ensuring high MTBE selectivity (up to 94% at 413 K) [75]. 

Usually, acid-activated clays are used in the process. These clays are manufactured from inactive bentonite and montmorillonite clays by milling, activating with a mineral acid, usually sulfuric acid (Norris, 1964) and washing and drying to a moisture content of 10-15%. Particle sizes range from 10-15% above 80 xm to 30-40% below 20 xm according to Patterson (1976). 

The use of acid-activated clay is essential in bleaching oils containing chlorophyll. Wettstrom (1972) indicates that acidic conditions destabilize the pigments. Carbon black is also used for removal of chlorophyll (Norris, 1964), but its use is much more costly. 

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