Adsorption on carbon

N2 as adsorbate, was quite similar to that for N2 on a directly prepared and probably amorphous ice powder [35, 141], On the other hand, N2 adsorption on carbon with increasing thickness of preadsorbed methanol decreased steadily—no limiting isotherm was reached [139]. 

Although the turpentine is largely desulfurized in the stripping stage and again in the fractionation stages, many appHcations for a- and P-pinene requite further desulfurization. Such methods involve adsorption on carbon, hypochlorite treatment, hydrogen peroxide treatment, treatment with metals, or a combination of techniques (6—15). 

Adsorption. Adsorption (qv) is an effective means of lowering the concentration of dissolved organics in effluent. Activated carbon is the most widely used and effective adsorbent for dyes (4) and, it has been extensively studied in the waste treatment of the different classes of dyes, ie, acid, direct, basic, reactive, disperse, etc (5—22). Commercial activated carbon can be prepared from lignite and bituminous coal, wood, pulp mill residue, coconut shell, and blood and have a surface area ranging from 500—1400 m /g (23). The feasibiUty of adsorption on carbon for the removal of dissolved organic pollutants has been demonstrated by adsorption isotherms (24) (see Carbon, activated carbon). Several pilot-plant and commercial-scale systems using activated carbon adsorption columns have been developed (25—27). 

The models of Matranga, Myers and Glandt [22] and Tan and Gubbins [23] for supercritical methane adsorption on carbon using a slit shaped pore have shown the importance of pore width on adsorbate density. An estimate of the pore width distribution has been recognized as a valuable tool in evaluating adsorbents. Several methods have been reported for obtaining pore size distributions, (PSDs), some of which are discussed below. 

Competitive adsorption on carbon was also studied. The results are shown in Figure 34.8. The product PG competitively adsorbs to carbon more readily than the starting material. This can have implications in reaching full conversion and on product stability. The impact of the relative adsorption is alleviated under continuous flow reactor conditions where we are able to achieve high conversion and high yield. A full accounting of the adsorption work will be the subject of a later publication. 

The process making use of adsorption on carbon involves first contacting a pregnant leach liquor with the adsorbent (activated carbon) and then stripping the species adsorbed on it. Activated carbon is a widely recognized as a metallurgical reagent that has found a number of industrial applications. 

The adsorption action of activated carbon may be explained in terms of the surface tension (or energy per unit surface area) exhibited by the activated particles whose specific surface area is very large. The molecules on the surface of the particles are subjected to unbalanced forces due to unsatisfied bonds and this is responsible for the attachment of other molecules to the surface. The attractive forces are, however, relatively weak and short range, and are called Van der Waals forces, and the adsorption process under these conditions is termed as a physical adsorption (physisorption) process. In this case, the adsorbed molecules are readily desorbed from the surface. Adsorption resulting from chemical interaction with surface molecules is termed as chemisorption. In contrast to the physical process described for the adsorption on carbon, the chemisorption process is characterized by stronger forces and irreversibility. It may, however, be mentioned that many adsorption phenomena involve both physical and chemical processes. They are, therefore, not easily classified, and the general term, sorption, is used to designate the mechanism of the process. 

Zuttel, A., P Sudan, P. Mauron, P Wenger, Model for the hydrogen adsorption on carbon nanostructures. Mater. Sci. Process. Appl. Phys. A 78, 941-946,2004. 

Analytical methods for detecting phenol in environmental samples are summarized in Table 6-2. The accuracy and sensitivity of phenol determination in environmental samples depends on sample preconcentration and pretreatment and the analytical method employed. The recovery of phenol from air and water by the various preconcentration methods is usually low for samples containing low levels of phenol. The two preconcentration methods commonly used for phenols in water are adsorption on XAD resin and adsorption on carbon. Both can give low recoveries, as shown by Van Rossum and Webb (1978). Solvent extraction at acidic pH with subsequent solvent concentration also gives unsatisfactory recovery for phenol. Even during carefully controlled conditions, phenol losses of up to 60% may occur during solvent evaporation (Handson and Hanrahan 1983). The in situ acetylation with subsequent solvent extraction as developed by Sithole et al. (1986) is probably one of the most promising methods. 

R. Strobel, L. Jorissen, T. Schhermann, V. Trapp, W. Schutz, K. Bohnhammel, G. Wolf, J. Garche, Hydrogen adsorption on carbon materials. J. Power Sources, 84(2) (1999) 221-224. 

FIG. 7.18 Adsorption on carbon from the ethanol-benzene system. The ordinate equals the total number of moles of solution times the change in solution mole fraction per unit weight of carbon. (Data from F. E. Bartell and C. K. Sloan, J. Am. Chem. Soc., 51, 1643 (1929).)... 

In either approach, the selection of isolation (e.g., solvent extraction, adsorption on carbon and synthetic resins) and concentration (e.g., lyophilization, vacuum distillation, reverse osmosis, ultrafiltration) methods is of paramount importance in properly assessing the potential toxicity of waterborne organics. A comprehensive literature review on the development and application of these and other methods to biological testing has recently been published by Jolley (3). 

Tang, Q. Wang, Y.-L. Chang, and H. J. Dai, An investigation of the mechanisms of electronic sensing of protein adsorption on carbon nanotube devices , Journal of The American Chemical Society 126, 1563 (2004). 

Figure 3.4 Surfactant adsorption on carbon black, T = 298 K, surface area = 1150m2g 1 (BET) (reproduced with permission [5]).

The process of adsorption on carbon is applicable to wastewaters and polluted air. Treated waters may be suitable for reuse in industrial processes and can be discharged safely to the sewer system if removal efficiencies are high enough. Hazardous constituents of no commercial value that are removed may be disposed in burial sites after they have been stabilized. The high capacity of activated carbon for many compounds is attributable to the large surface area of the carbon (500-1500 m2 g-1). 

An example of a weak perturbation is adsorption on carbon nanotubes 17a) (Fig. 2b), where it is shown that the rotational line is broadened and split. The / = 1 level is threefold degenerate Mj = 0, + 1), and the interaction with the nanotubes has partially lifted the degeneracy. 

To be a promising candidate for CO2 foam, the surfactant loss by adsorption, partitioning and emulsion formation must be low. In general, anionic surfactants have low adsorption on sandstones and high adsorption on carbonates, whereas the reverse is true for nonionics ( ). Cationic surfactants are not considered because of their high adsorption on many surfaces. 

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