Commercially available adsorbents

Selec ted data on commercially available adsorbents and ion exchangers are given in Tables 16-5 and 16-6. The purpose of the tables is twofold to assist the engineer or scientist in identifying materials suitable for a needed apphcation, and to supply typical physical property values. 

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... 

The designer now needs to make some estimates of mass transfer. These properties are generally well known for commercially available adsorbents, so the job is not difficult. We need to re-introduce the adsorber cross-section area and the gas velocity in order to make the required estimates of the external film contribution to the overall mass transfer. For spherical beads or pellets we can generally employ Eq. (7.12) or (7.15) of Ruthven s text to obtain the Sherwood number. That correlation is the mass transfer analog to the Nusselt number formulation in heat transfer ... 

Diazinon has a finite vapor pressure (see Chapter 3) and thus will be present in the air. A method for diazinon in air has been reported that is based on the use of polyurethane foam (PUF) to adsorb the pesticide from the air as the air is pulled through the PUF (Hsu et al. 1988). The PUF is then Soxhlet-extracted and the extract volume reduced prior to capillary GC/MS analysis. An LOD of 55 ng/m3 (5.5 m3 sample) and recovery of 73% were reported. Another study was described in which the diazinon levels in indoor air were monitored following periodic application of the pesticide for insect control (Williams et al. 1987). In this method, air is pulled through a commercially available adsorbent tube to concentrate diazinon. The tube is then extracted with acetone prior to GC/NPD analysis. No data were provided for the LOD, but recoveries in excess of 90% were reported at the 0.1 and 1 pg/m3 levels. This paper also indicated that diazinon can be converted to diazoxon by ozone and NOx in the air during the sampling process. 

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... 

A number of specialty companies have and are continuing to develop adsorbents to collect organic molecules from air samples. Industrial chemicals resulting, from syntheses or used in production processes, pesticides and emissions from exhaust towers are monitored routinely with commercially available adsorbents. Personnel monitoring can be accomplished without a pump using a system composed of a porous membrane through which air diffuses and compounds of interest are collected by an adsorbent. 

In paper chromatography we use filter paper, marketed for this purpose. It comes usually in the form of a 2-5 cm-wide tape, from which a strip of the necessary length can easily be cut. The more modern technique of thin layer chromatography (TLC), makes use of thin sheets of aluminium oxide, silica-gel, cellulose or some other material, supported by a metal sheet or a polymer. Chromatographic thin layers can be prepared in the laboratory from commercially available adsorbents. A thick suspension of these is made with water (usually a 2 1 w/w mixture of water adsorbent is made up) and this is then spread on a metal plate with a suitable spreader device. Techniques vary from device to device, and the instructions of the manufacturer should be followed whenever thin layer plates are to be prepared. Ready-made thin layer sheets are also available commercially. These contain the active material spread on a plastic support. Thin-layer chromatographic materials, especially ready-made plates, are much more expensive than chromatographic paper, but normally offer faster and sharper separations than the paper. The procedures described in Section VI.20 can be carried out both on a slow chromatographic paper (e.g. Whatman No. 1) or on a cellulose thin layer (e.g. Whatman cellulose). 

When a separation can be effected by a purely adsorptive mechanism (GSC), various adsorbants and porous polymers are used. Commercially available adsorbants include silica gel, activated charcoal, and molecular sieve materials. These adsorbants are used mainly for the analysis of gases and low-molecular-weight, low-boiling compounds. ... 

Adsorption allows the selective collection and concentration onto solid surfaces of specific dissolved molecules from the broth. Adsorption can be non-specific, for those mechanisms based on polar, van der Waals and ionic interactions, or highly selective for affinity binding based on biochemical means (1,8) Commercially available adsorbants are generally granular porous particles to provide extensive surface area, with void volumes approaching 30-50% of the whole particle. Pore diameters are usually less than 0.01 mm. 

The physical characteristics of the LSX pellets are both similar to and different from those of typical pelletized X zeolites. In both cases the total nonzeolltlc pore volume 1s about 0.25 cc/g, with a bulk density of about 0.65 g/cc on a dry basis. Flowever, the LSX pellets have a substantially larger macroporosity than commercially available adsorbents. Median pore diameters for the self-bound adsorbents vary from 1.5 to 5.0 ym whereas those for typical pelletized X adsorbents are around 0.1 ym. 

Limited number of commercially available adsorbents for gas-solid chromatography... 

In the case of petroleum gas and liquid feeds the usage of activated carbon impregnated with a catalyst, e.g. sulphur (for gasses) or iodide (for liquids) is very often practiced (O Dowd et al. 2006). Moreover, it is also proven that ionic liquids, particularly Solid Supported Ionic Liquids (SSILs), can capture all types of mercury in a single step more efficiently than other techniques (Mahpuzah Abai 2011). SSILs can adsorb mercury three times more than other commercially available adsorbents even without modifications to the plant infrastructure (Shariff 2011). 

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