Activated adsorption system

Figure Bl.25.12 illustrates the two scattering modes for a hypothetical adsorption system consisting of an atom on a metal [3]. The stretch vibration of the atom perpendicular to the surface is accompanied by a change m dipole moment the bending mode parallel to the surface is not. As explained above, the EELS spectrum of electrons scattered in the specular direction detects only the dipole-active vibration. The more isotropically scattered electrons, however, undergo impact scattering and excite both vibrational modes. Note that the comparison of EELS spectra recorded in specular and off-specular direction yields infomiation about the orientation of an adsorbed molecule.

Other types of regenerators designed for specific adsorption systems may use solvents and chemicals to remove susceptible adsorbates (51), steam or heated inert gas to recover volatile organic solvents (52), and biological systems in which organics adsorbed on the activated carbon during water treatment are continuously degraded (53). 

Engineering Considerations To effect the good engineering design of an activated carbon adsorption system, it is first necessary to obtain information on the following the actual cubic feet per minute (ACFM) of air to be processed by the adsorber, the temperature of gas stream, the material(s) to be absorbed, the concentration of the material to be adsorbed, and if the intended application is air pollution control such as odor control - then the odor threshold of the material to be adsorbed. In addition, data is needed on the presence of other constituents in the gas stream, and whether or not solvent recovery is economical. 

Adsorption beds of activated carbon for the purification of citric acid, and adsorption of organic chemicals by charcoal or porous polymers, are good examples of ion-exchange adsorption systems. Synthetic resins such as styrene, divinylbenzene, acrylamide polymers activated carbon are porous media with total surface area of 450-1800 m2-g h There are a few well-known adsorption systems such as isothermal adsorption systems. The best known adsorption model is Langmuir isotherm adsorption. 

The adsorption systems involve the adsorption of the pollutant on the surface of a solid. The solid can then be regenerated by passing hot gases such as steam through the system. A concentrated pollutant is then recovered hopefully it can be converted into a by-product or fuel. The most common adsorbents are activated carbon, silica gel, alumina, and molecular sieves.29... 

It adequately treats the low volumes of offgases produced in the process, including those from the SCWO reactors, through catalytic oxidation and activated carbon adsorption systems. 

Adsorption systems make use of the fact that VOCs are attracted to and will adsorb to (attach to the surface of) certain special materials, the most common of which is activated charcoal. Activated charcoal consists of finely divided particles of charcoal. Flue gases containing VOCs are passed through a chamber and over a bed of the adsorbent, where they collect on its surface. The system may be designed such that the VOCs can then be removed from the... 

Adsorbent beds used in the PADRE process have been recycled on a test stand more than 2000 times with no measurable loss of adsorption capacity. Also, the PADRE resin has a relatively high tolerance for water vapor, allowing efficient treatment of airstreams with a relative humidity of greater than 90%. These two advantages make the PADRE process a cost-effective on-site treatment technology when compared to traditional activated carbon systems. 

A precise definition of chemisorption for all the observed adsorption systems is at present difficult, because the concept of chemical forces is by no means clear. Furthermore, it is difficult to decide how far the influence of strong dipole forces enters into the general phenomenon of chemisorption. Furthermore, the requirement of an activation energy cannot be considered as a positive criterion for chemisorption processes. Engell and Hauffe (16-18) have limited their theoretical considerations of the chemisorption, on a solid, to particles in the form of ions (ionosorption), and similarly this review will deal with this type of chemisorption. 

The most common adsorption systems consist of silica gel or alumina adsorbents in association with an organic solvent system. The adsorbent can exert a considerable influence on the separation of compounds. Alumina and silica gel, for example, have significantly different properties and can result in quite different separations. Activation of the adsorbent also influences sample retention. The presence of water on the adsorbent decreases the adsorbent activity due to blockage of active sites. If large quantities of water are present, a partition system may be set up which may extensively change the retention times due to the different chromatographic principle involved. Table 2.1 compares results obtained for the separation of the insecticide carbaryl (Sevin) and its hydrolysis product 1-naphthol on alumina and silica gel. Comparisons between activation and deactivation are made. The results show that separation of the two components is reversed with the two adsorbents examined. In most cases, activation of the plates caused the/ f values to increase relative... 

---