Silica gel as adsorbent

Naphtha reformate and other close-boiling hydrocarbons 197 Silica gel as adsorbent... 

Introducing adsorbents into a supercritical fluid extraction system is an alternative attractive method to improve the selectivity for the citrus oil processing. Several applications using silica gel as adsorbent have been reported in the last decade [1-3]. Yamauchi and Saito [3] fractionated lemon peel oil into 3 fractions with gradual increase in pressure by supercritical fluid chromatography, where terpene rich fraction, ester rich, and alcohol and aldehyde rich fraction were obtained at 10 MPa, 20 MPa, and 20 MPa with ethanol as a cosolvent,... 

Energy efficient gas separation processes, particularly in the chemical and petrochemical industry, have been a subject of increased attention in recent years. This is due to the high energy input, and thus high cost of industrial gas separations by conventional processes, such as cryogenic distillation and/or absorption. Adsorption processes, based on activated carbon or silica gel as adsorbents, have proven reliable, efficient and cost effective for a number of industrial gas separations. The search for a suitable adsorbent is the first step in this [1, 2]. 

Burwell, R.L., Modified silica gel as adsorbents and catalysts, Chemtech, June, 370-377 (1974). 

Residues obtained from filtrates of multiple recrystallizations of 6B were combined and subjected to column chromatographic separation with silica gel as adsorbent and chloroform and ethanol, respectively, as eluants. Residual quantities of 6B separated out in the first fraction followed by a compound showing the presence of both carbonyl and nitro absorption frequencies in the IR spectrum. This was followed by 8B (0.5%) in the pure form. The mixture of isomers had m.p. 155-60°C. Anal. Calcd. for C12H20N2O3 C, 60.00 H, 8.33 N, 11.66. Found C, 60.08 H, 8.57 N, 11.45. u max cm i 3300-... 

The reversed phase TLC coupled with Fast Atom Bombardment spectrometric method has been used for identification and separation of 27 food dyes consisting of twelve permitted for use in food and fifteen unlawful dyes in Japan using Cig-modified silica gel as adsorbent and using two mobile phases. The method was successfully applied for the identification of unlawful dyes in imported foods (150). The Revalues along with mobile phases used for these dyes are recorded in Table 16. 

Quinoxaline 1,4-dioxides have also been prepared by condensation reactions carried out on the surface of solid catalysts such as silica gel, " molecular sieves, " or alumina. " As a representative example, " BFO 1 and the P-dicarbonyl compound 16 were combined with silica gel in methanol. The excess methanol was removed by evaporation and the silica gel with adsorbed reagents was allowed to stand for two weeks without drying. The quinoxaline 1,4-dioxide 17 was obtained in 90% yield after elution from a silica gel column. 

Pyridine adsorbed on silica gel as a function of temperature (°C). P = 1.86 x 10 2bar. (Reprinted with permission from Review of Scientific Instruments, 46 (1335), 1975. Copyright by the American Institute of Physics.)... 

A. K. Chakraborti and R. Gulhane, Perchloric acid adsorbed on silica gel as a new, highly efficient, and versatile catalyst for acetylation of phenols, thiols, alcohols, and amines, Chem. Commun., 15 (2003) 1896-1897. 

The enantioselective binding properties of certain chiral crown ethers have been employed in the resolution of amino add racemates. The racemic amino ester is adsorbed onto silica gel as its ammonium salt and eluted by a chloroform solution of the chiral crown ether. An excellent separation of the two enantiomers is achieved by this method (74JA7100). 

Silica Gel. Silica gel is a polar adsorbent, its surface containing hydroxyl groups. Thus polar substances have a strong attraction toward silica gel. Since water is highly polar, silica gel retains atmospheric moisture, sometimes preferentially over other substances. This affinity for moisture limits the use of silica gel, although in a dry environment it would be an excellent sorbent. The compounds for which our laboratories have validated methods using silica gel as a collection medium are listed below ... 

Adsorption of mercury. All chemicals used were Merck or Baker analytical quality reagents, unless stated otherwise. From the commercially available adsorbents the following were used silica gel 60 A porosity, 0.063-0.200 mm particle size (Merck) charcoal 0.3-0.5 mm particle size, gas-chromatographic quality (Merck) alumina R Woelm hydrous zirconium oxide HZ0-1, 100-200 mesh, (Bio-Rad). Except for zirconium phosphate, which was prepared according to Amphlett ( ), all other sorbents were prepared by coating (precipitation) on acid-purified silica gel, as described in (1 ). The Si0 -NH was prepared according to Leyden et al (11). L... 

The checkers found that alumina was not sufficient to remove the NBuJHS04 and used silica gel as the chromatography adsorbent. 

Silica gel is an adsorbent for aromatics and has found use in extracting aromatics from refinery streams. Silica gel is manufactured amorphous silica that is extremely porous and has the property of selectively removing and holding certain chemical compounds from mixtures. For example, silica gel selectively removes aromatics from a petroleum fraction, and after the nonaromatic portion of the fraction is drained from the silica gel, the adsorbed aromatics are washed from the silica gel by a stripper (or desorbent). Depending on the kind of feedstock, xylene, kerosene, or pentane may be used as the desorbent. 

In the analytical field, modification implements the use of silica gel as a selective adsorbent for gases, liquids and metals. Modified silica is widely used as a stationary phase in various types of chromatography and as a metal ion sorbent. The use of silica as a support is restricted to the pH 1-8 range, due to the instability of the silica structure in basic conditions. For the separation of basic solutions, polymeric support materials are used. 

Figure 12.5 Irreversibly adsorbed and/or chemisorbed ammonia on silica gel as a Junction of the reaction temperature, with and without TCS modification.

In tandem with the use of supercritical carbon dioxide, in ester synthesis employing Candida Antarctica lipase B, adsorbed on silica gel, as the esterification catalyst under minimum water conditions.50... 

When the composite-matrix is formed with a polystyrene solution as a dispersion medium, the self-assembly of silica particles is influenced by the adsorption of macromolecules on their surface. During adsorption, both solitary macromolecules and their aggregates transfer simultaneously onto the adsorbent surface. Depending on solution concentration, not only the conformation of adsorbed molecules but also the number and size of macromolecular aggregates in the solution change on adsorption. This leads to the formation of complex-shaped structures, which are linked by a system of nonvalent interactions and consist of polymeric-inorganic blocks[8,14] this is of interest in the preparation of a nanostructured medium (polystyrene-silica gel) as a precomposite for the fabrication of carbon structures in a matrix of silica particles. 

The use of adsorbents in conjunction with appropriate conditions for supercritical CO2 extraction enhances the efficiency of cholesterol extraction. Selective removal of 97% of cholesterol has been achieved with the use of silica gel as an in-line adsorbent (Huber et ah, 1996). Removal of 96% of cholesterol in milk fat fractions can be achieved by a combined supercritical C02 extraction and an alumina adsorption process (Mohamed et al., 1998). 

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