Silicagel properties

Silicagel is built of 99% SiC>2, while the rest are OH groups together with changing amounts of integrated water. The properties of Silicagel are shown in Table 31. 

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... 

Silicagel is also called silica or bare silica. Its adsorptive properties depend on the hydroxyl groups attached to surface silicon atoms. Silicagel has a maximum silanol density of 8.0 yumolcs/ m2. Many of these silanols are buried deep in the porous structure and are available only to the smallest analytes. Silanols are either isolated, geminal, or vicinal they can be distinguished by means of Si solid-state nuclear magnetic resonance (NMR). The surface also contains siloxane bonds (Si-O-Si), which are considered hydrophobic. 

Normal-phase liquid chromatography can be used to separate interfering compounds from SVOCs, pesticides, and PCBs. Three classical adsorbents—Florisil, alumina, and silicagel—are commonly used, although many other polar adsorbents are available. Table 15.7 shows some of the properties and characteristics of these adsorbents. Prior to the cleanup, the sample extract must be exchanged to a solvent that is compatible with the chromatographic separation. Because they are nonpolar, hexane and methylene chloride are common choices. 

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