Amorphous synthetic silicas, production

Amorphous Synthetic Silica Products in Powder Form. Production and Characterisation, Degussa Technical Bulletin Pigments No.32, Degussa AG, Frankfurt, Germany, 1980. 

Kimberlin applied for a patent in February 5, 1957 which was issued on February 14, 1961 and was assigned to Esso Research Engineering Co. 80). This patent taught the reduction of sodium content by base exchange, a process similar to that used with amorphous synthetic silica-alumina catalysts. This patent included in the body, but not the claims, the use of base exchange with rare earths. The court held that Kimberlin s patent indicated that (80) (1) the zeolite should be used as the sole catalyst in the cracking zone, (2) that crystalline materials adversely affect the catalytic performance of conventional amorphous catalysts ["By whatever means prepared, the final catalyst was amorphous and, indeed, if any crystalline material were present in the final product, hydrocarbon conversion was seriously adversely affected and... 

Approximately 40% of synthetic amorphous silica production is in Europe, followed by North America at 30%, and Japan at 12%. Although deposits of naturally occurring amorphous silicas are found in all areas of the wodd, the most significant commercial exploitation is of diatomaceous earth in industrialized countries (see Diatomite). This is because of the high cost of transportation relative to the cost of the material. Woddwide manufacturers of amorphous silica products are listed in Table 2. 

The common availability of silica is not the sole reason for its extensive use. Probably, it is the chemical inertness and durability of silica which determined its popularity. The fillers discussed here include not only natural minerals but also a variety of synthetic products. Natural products can be divided into crystalline and amorphous. Crystalline silica fillers include sands, ground silica (or silica flour), and a form of quartz - tripoli, whereas the amorphous types include diatomaceous earth. 

Silicates—These chemically inert synthetic amorphous silica adsorbents have an affinity for polar contaminants. The surface area, porosity, and moisture content of the silica adsorbents provide them the capability of adsorbing secondary oxidation products (aldehydes, ketones), phosphatidic compounds, sulfur compounds, trace metals, and soap. Moisture functions to hold the pores open and aid in the attraction of the polar contaminants. Most of the synthetic silicas do not have significant direct adsorption capabilities for carotenoid or chlorophyll compounds, but the removal of the other impurities enhances the efficiency of the bleaching earths (Young, 1990). 

The aim of this chapter is more limited the emphasis is to provide an overview of the uses of synthetic silica gels and precipitated silicas that are of significant commercial importance. Excluded from this discussion are naturally occurring silicas, including products such as diatomaceous earth and so-called amorphous silica minerals (which are actually microcrystalline). Also excluded are fumed and arc silicas, forms of synthetic silica made at high temperature (in contrast to silica gels and precipitated silicas, which are generally made in aqueous solution and... 

John Gyann in his US Patent (4,764,384, 1988) proposed a blend of amorphous silica, synthetic amorphous magnesium silicate, diatomaceous earth and synthetic silica alumina for rejuvenating spent frying oil. In this invention, the inventor claims that the adsorbent would remove some free fatty acids and other oil breakdown products. It does not clearly specify if the adsorbent also removes the soap that is formed during adsorption due... 

The primary differentiation among silica products is their natural vs. synthetic origin, which translates to a division between crystalline and amorphous forms. 

SBR is the most widely used synthetic elastomer. It is an amorphous random copolymer consisting of a mixture of l.2, cis and trans isomers. Cold SBR produced at —20 C consists of 17% 1,2. 6% cis and 77% trans isomers of polybutadiene. This commercial product has a Tt of -60 C, an index of refraction of 1.534S, and a coefficient of linear expansion of 66 X 10 s cm/ cm C. Because of the high percentage of the trans isomer, it is less flexible and has a higher heat buildup, when flexed, than Hevea rubber. Although carbon black-filled or amorphous silica-filled SBR has useful physical and mechanical properties, the SBR gum rubber is inferior to Hevea rubber. 

The yield of the reaction (Table 1) clearly depends or the nature of the solid and on the experimental conditions (temperature, time). Thus, with silica and alumina, amorphous solids with a relatively low acidity, the acetophenone oxime molecule reacts with a very low yield, being the only reaction product the hydrolysis one, acetophenone. With the synthetic mixed oxide silica-alumina, that possesses simultaneously BrOnsted and Lewis acidic centres, the conversion is quantitative, being also the major product the hydrolysis one (3), when the reaction is carried out at 160°C. 

Silicon Dioxide occurs as an amorphous substance that shows a noncrystalline pattern when examined by X-ray diffraction. It is produced synthetically, either by a vapor-phase hydrolysis process, yielding fumed silica, or by a wet process, yielding precipitated silica, silica gel, colloidal silica, or hydrous silica. Fumed silica is produced in an essentially anhydrous state, whereas the wet-process products are obtained as hydrates or contain surface-adsorbed water. 

R. C. Hansford (Union Oil Co. of California, Brea, Calif. 92621) To what extent might some amorphous silica-alumina be responsible for the poor selectivity—i.e., are the synthetic products completely crystalline ... 

Amongst the various synthetic routes, aldehydes and ammonia condensation is commercially proven success (1-8). In view of tremendous potentiality for commercial production and meagre information available in literature, studies were undertaken in this investigation to develop active, seleetive and stable catalyst based on amorphous silica-alumina or crystalline aluminosilicate (zeolite). Further, an attempt has been made to correlate the activity with the acidity of the catalyst. 

Until 1985 silicas were usually divided into two groups natural and synthetic. Most of the naturally occurring SiC>2 modifications are crystalline, but this group also includes amorphous or mostly amorphous products, such as diatomaceous earth or kieselguhr. However, when the observations made at the end of the introduction are considered, this classification no longer proves sufficient, as fly ashes and silica fume are also synthetically produced, although not deliberately. These airborne dusts are not harmless (22). 

Special effects have also been established during the improvement of the free-flow properties of products in powder form. Unfortunately, it is not yet possible to predict under which conditions a hydrophobic synthetic amorphous silica will produce better results than a hydrophilic (i.e., untreated) one. A similar situation exists in the area involving the thickening of technically important resins [e.g., special unsaturated polyester or epoxy resins (63)]. 

In common use are three principal materials of silica one natural (both crystalline and amorphous) and two so-called synthetic, products of thermal process (fumed silica grades) and wet process (precipitated silica). Particles of silica commonly have a spherical shape. 

Precipitated silica (silica P) abrasive SiOj have been introduced in toothpaste formulation in the 1970s. They are synthetic, noncrystaUine, or amorphous silica. They represent -80% of the world production of synthetic amorphous silica. Variation in the particle size allows the control of the abrasivity and the thickness of the product. Amorphous silica is obtained by reaction of a sodium silicate solution at pH >7 with an add such as H2SO4 or HCl, according to the following reaction ... 

EFSA (2004) Opinion of the scientific panel on dietetic products, nutrition and allergies on a request from the commission related to the Tolerable Upper Intake level of silicon. EFSA J 60 1-11 Fruijtier-Polloth C (2012) The toxicological mode of action and the safety of synthetic amorphous silica - a nanostructured material. Toxicology 294 61-79 Gitelman HJ, Alderman FR, Perry SJ (1992) Silicon accumulation in dialysis patients. Am J Kidney Dis 19(2) 140-143... 

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