Adsorbents silicagel

A 0.6 g (0.006 mol) of CICH2COOH was added to the solution of the solution of 2 g (0.0058 mol) FK-IG (I) in 30 ml dry benzene. The reaction mixture was stirred at room temperature for 30 min, than was filtered by layer AI2O3. The filtrate consisted of two compounds, which were separated by column chromatography (adsorbent-silicagel (100-250), solvent-hexane, eluant-ether/hexane 1 4) were formed two following products -V and VI - di (l-ferrocenyl-l-phenyl-2-5Ui-4-pent3m)ether ... 

The most common classes of solid adsorbents are Zeolites and Silicagels. The main difference between the two is the way they are built. Zeolites have a crystalline structure and therefore a certain pore size. Silicagel have a pore... 

Concerning the application of these adsorbents as thermal energy storages the amount of water, which can be adsorbed is the most important property. Figure 238 shows the maximum water uptake of some commercially available adsorbents. Zeolite A can reach 25% and Zeolite 13X up to 32% of its dry weight. Narrow pore Silicagel can adsorb 38% water. Two special adsorbents Sizeo, which is a mixture of Zeolite and Silicagel, and SWS, which is a wide... 

Purification by pressure column chromatography on silicagel is conducted as follows. A glass column (inner diameter 5 cm, length 51 cm) is filled with a slurry of silica (450 g of silicagel, Acros, 0.035-0.070 mm, pore diameter 6 nm) in 95 5 (v v) CH2Cl2/acetone. A 3-g portion of cmde [AsPl JL is dissolved in a minimum amount of solvent and adsorbed on the top of the column. The column is connected with a membrane pump (output pressure 1.6 bar) and then eluted at a flow rate of about 180 mL/min. The violet fraction is collected and evaporated on a rotary evaporator. This chromatographic separation on the whole lasts 8 h. 

In contrast to the work quoted above, we studied not only the adsorption of molecules from the gas phase (for porous glass as adsorbent), but also from their solutions in CC14 (for silicagel and alumo-silicagei). Some preliminary experiments in that direction have been made with porous glass by V. Baikov in 1954. His data are reproduced in parentheses in Table I. 

Fig. 4. Position of the N—H maxima for dUJerent compounds —in earbontetra-chloride (or chloroform) solutions — adsorbed on silicagel (or alumosilieagel)...

Crystalline g-phenylpropiophenone is not phosphorescent at room temperature. Similarly, adsorption on silicagel does not lead to significant phosphorescence. It would thus appear that a channel structure is essential. In fact, channel (or pore) dimensions also appear to be quite important for example, when g-phenylpropio-phenone is adsorbed on Mordernite, a zeolite with 9A pores, no luminescence can be detected (15). 

Acetone. The spectra of acetone surface complexes at low OH coverages of zeolites are given in Fig. 4. For comparison, the spectrum of acetone adsorbed on weak silanol groups of silicagel is also displayed. The spectral features found can be divided into three groups belonging to... 

Table 6. Dependence of Retention on the Concentration of the Counter-ion u> Adsorbent silanized silicagel Merck ...

Tetmffuoroethylem. Polymerization of tetrafluwoethylene adsorbed on varirars sorbents including silicagel, NaY zeolites and CaA zerolites is initiated by y-irradiation. The thre old temperature for the polymerization of the adsorbed monomer increases in the order silicagel < NaY zeoUtes < CaA zeolites... 

A further variation of classical PTC is gas-solid PTC. In this technique a continuous flow of the gaseous substrate passes through a fixed bed of the reacting salt and of a thermally stable catalyst, normally a phosphonium salt, eventually adsorbed on silicagel This technique has been applied to simple nucleophilic dis-... 

To establish the interaetion of the impregnating solutions with the surface of silica supports, Terorde measured the amount of water required to completely remove different iron salts applied onto the surface of silicagel in a column chromatograph [41], It appeared that an elution volume of water of 5.0 ml was required to remove the iron ammonium citrate, and of 6.2 ml to remove the Mohr s salt. Iron(III) chloride called for an elution volume of 6.3 ml, and iron(III) nitrate for a volume of 7.7 ml. Apparently, the iron species in the initially impregnated solution of iron ammonim citrate does not interact strongly with the silica surface. The relatively small interaction of the iron(III) complex of citric acid with the surface of silica indicates that the presence of the citric acid affects the adsorbed layer of water molecules that remains within the partially dried impregnated support. A thicker, less mobile layer of water molecules, citric acid anions, and iron(III) ions remains than without citric acid, where a layer of about six fairly mobile water molecules is present. 

Thermal desorption is the method of choice to monitor air pollution. A known amount of air is drawn through an adsorbent tube filled with activated carbon, Tenax, silicagel, or mixtures of these. Analytes of interest are trapped and concentrated on the adsorbent. The ad.sorbenl tube is sealed and transported to the laboratory where it is installed in the thermal desorption unit. An example of a thermal desorption unit is shown in Figure 33. After the adsorbent tube is placed in the desorption module, the carrier gas is directed over the adsorbent, which is heated from room temperature to 250-300 "C. Since thermal desorption is a slow process, the solutes are focused by cold trapping on a fused silica trap. The cryogenic trap is then heated rapidly to transfer the sample to the column. The method works well for apolar and medium-polarity components in air. Highly polar solutes are very hard to desorb, and other sampling methods must be selected,... 

PSA and VSA use a column filled with a molecular sieve, typically activated carbon, silicagel, alumina, or zeolite, for differential adsorption of the gases CO2 and H2O, alloeing CH4 pass through [47, 49]. The molecules are adsorbed loosely in the cavities of the molecular sieve and not irreversible bound [46]. It is a cyclic batch process where adsorption is performed on a relatively higher pressure (around 800 kPa) and desorption (regeneration) at lower pressure [51]. H2S,... 

Metal Oxides. These include (a) silicagel, which is a specific type of adsorbent because there are free hydroxyl groups on the surface (polar molecules are easily separated on these materials, and wide-pore silicas with homogeneous surfaces are used for analytical gas-solid chromatography ) and (b) alumina. These columns can be easily baked out to remove contaminants and reused with good reproducibility. 

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