Adsorbed material

Many solids show marked swelling as a result of the uptake of a gas or a liquid. In certain cases involving the adsorption of a vapor by a porous solid, a linear relationship exists between the percentage of linear expansion of Ae solid and the film pressure of the adsorbed material [134, 135]. 

A logical division is made for the adsorption of nonelectrolytes according to whether they are in dilute or concentrated solution. In dilute solutions, the treatment is very similar to that for gas adsorption, whereas in concentrated binary mixtures the role of the solvent becomes more explicit. An important class of adsorbed materials, self-assembling monolayers, are briefly reviewed along with an overview of the essential features of polymer adsorption. The adsorption of electrolytes is treated briefly, mainly in terms of the exchange of components in an electrical double layer. 

Solid-Phase Extractions In a solid-phase extraction the sample is passed through a cartridge containing solid particulates that serve as the adsorbent material. For liquid samples the solid adsorbent is isolated in either a disk cartridge or a column (Figure 7.17). The choice of adsorbent is determined by the properties of the species being retained and the matrix in which it is found. Representative solid adsorbents... 

New Adsorbent Materials. SihcaUte and other hydrophobic molecular sieves, the new family of AlPO molecular sieves, and steadily increasing families of other new molecular sieves (including stmctures with much larger pores than those now commercially available), as well as new carbon molecular sieves and pillared interlayer clays (PILCS), will become more available for commercial appHcations, including adsorption. Adsorbents with enhanced performance, both highly selective physical adsorbents and easily regenerated, weak chemisorbents will be developed, as will new rate-selective adsorbents. 

Regardless of method, desorption is never complete. Adsorbent capacity is always less following regeneration than it is on initial loading of adsorbent. Some adsorbable materials undergo chemisorption they chemically combine with the adsorbent. An example is the Reinluft process (52) for removing SO2 from flue gas on activated carbon. The SO2 is attached to the carbon as sulfuric acid. Desorption occurs only upon heating to 370°C a mixture of CO2, evolved from the chemically bound carbon, and SO2 are driven off. 

In terms of membrane area used and doUar value of the membrane produced, artificial kidneys are the single largest appHcation of membranes. Similar hoUow-fiber devices are being explored for other medical uses, including an artificial pancreas, in which islets of Langerhans supply insulin to diabetic patients, or an artificial Uver, in which adsorbent materials remove bUinibin and other toxins. 

Of the four commercial processes for the purification of carbon monoxide two processes are based on the absorption of carbon monoxide by salt solutions, the third uses either low temperature condensation or fractionation, and the fourth method utilizes the adsorption of carbon monoxide on a soHd adsorbent material. AH four processes use similar techniques to remove minor impurities. Particulates are removed in cyclones or by scmbbing. Scmbbing also removes any tars or heavy hydrocarbon fractions. Acid gases are removed by absorption in monoethanolamine, hot potassium carbonate, or by other patented removal processes. The purified gas stream is then sent to a carbon monoxide recovery section for final purification and by-product recovery. 

For adsorbent materials, experimental tortuosity factors generally fall in the range 2-6 and generally decrease as the particle porosity is increased. Higher apparent values may be obtained when the experimental measurements are affected by other resistances, while v ues much lower than 2 generally indicate that surface or solid diffusion occurs in parallel to pore diffusion. 

Numerical values for solid diffusivities D,j in adsorbents are sparse and disperse. Moreover, they may be strongly dependent on the adsorbed phase concentration of solute. Hence, locally conducted experiments and interpretation must be used to a great extent. Summaries of available data for surface diffusivities in activated carbon and other adsorbent materials and for micropore diffusivities in zeolites are given in Ruthven, Yang, Suzuki, and Karger and Ruthven (gen. refs.). 

The escaping bubbles from the top of a bubble-fractionation column can carry off an appreciable quantity of adsorbed material in an aerosol of very fine film drops [various papers, J. Geophys. Res., Oceans Atmos., 77(27), (1972)]. If the residu solute is thus appre-ciablv depleted, Cj in Eq. (22-57) should be replaced with the average residual concentration. 

ANG tank design and the adsorbent materials chosen can help to minimize these problems. However, these alone may not provide a total solution to the... 

Thorpe, R.N., Heat transfer by forced convection in beds of granular adsorbent material for solid adsorption heat pumps. Ph.D. Thesis, University of Warwick, UK, 1996. 

The potential for use of chiral natural materials such as cellulose for separation of enantiomers has long been recognized, but development of efficient materials occurred relatively recently. Several acylated derivatives of cellulose are effective chiral stationary phases. Benzoate esters and aryl carbamates are particularly useful. These materials are commercially available on a silica support and imder the trademark Chiralcel. Figure 2.4 shows the resolution of y-phenyl-y-butyrolactone with the use of acetylated cellulose as the adsorbent material. 

Activated carbon in particular is very versatile as a filter media because it not only can physically separate out suspended solids, but it can adsorb materials. The adsorption process occurs at solid-solid, gas-solid, gas-liquid, liquid-liquid, or... 

Efficiency The effectiveness of the operational performance of an ion ex- changer. Efficiency in the adsorption of ions is expressed as the quantity of regenerant required to effect the removal of a specified unit weight of adsorbed material, for example, pounds of acid per kilogram of salt removed. 

Certain highly porous solid materials selectively adsorb certain molecules. Examples are silica gel for separation of aromatics from other hydrocarbons, and activated charcoal for removing liquid components from gases. Adsorption is analogous to absorption, but the principles are different. Layers of adsorbed material, only a few molecules thick, are formed on the extensive interior area of the adsorbent - possibly as large as 50,000 sq. ft./lb of material. 

Adsorption by surfaces is normally of little significance, except when the adsorbed material can change the perfotmance of the surface (e.g., its strength gh corrosion) or when the adsorbed contaminants can be reemitted to... 

Adsorber An adsorbent material used in the adsorption process. 

Bed depth The depth of adsorbent material through which the gas being treated passes,... 

Desorption The removal of adsorbed materials from a solid sorbent by the use of a solvent or the application of heat. Desulfurization The removal of sulfur from flue or other sulfur-containing gases. 

Mesopores Pores of diameters from 0.00005 mm to 0.005 mm that form the internal structure of an adsorbent material. 

By assuming a balhstic delivery of material (e.g., from the vapor phase or through directed evaporation) we obtain at least a qualitative picture for the various growth forms of a faceted crystal surface. We assume that the adsorbed material ( A ) behaves differently from the crystalline substrate ( S ). 

It has been found that the compound 8-geranoxy psoralen is present in citrus oils, particu-lariy lemon and lime oils. This compound can be isolated from the oil by a process which involves primarily absorption on an adsorbent material followed by elution with a suitable solvent. 

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