Phenols adsorption isotherms

Economy and Lin [340] investigated the phenol adsorption characteristics of high-surface-area activated carbon fibers Fig. 17b shows that their correlation was not nearly as good, but the role of surface chemistry was not invoked. Additional evidence that the agreement shown in Fig. 17a is more often the exception [439] than the rule is contained in the study of Dondi et al. [342], who u.sed a chromatographic method to determine low-concentration phenol adsorption isotherms on four different carbons, as well as in many other investigations (see, for example. Refs. 356, 382, 384, and 436). 

Peel and Benedek [407] published a useful review of reported phenol adsorption isotherms on a popular commercial activated carbon and concluded that the observed differences [as low as 100 vs. as high as 200 mg/g at 100 mg/L] are greater in magnitude than might reasonably be attributed to [variations in carbon properties and environmental conditions such as temperature, pH, and buffer... 

To demonstrate this phenomenon (Table 25.2), sample A was oxidized in order to increase its surface acidity. Heat treatment of the oxidized sample progressively decreased the surface acidity, mainly through the removal of carboxyl and phenolic groups [19]. A sample heat-treated at 950°C had no acidity, and its surface area was lower than that of an as-received sample. Phenol adsorption isotherms on these carbons are shown in Fig. 25.3. There was a large decrease in phenol uptake after oxidation. This phenol uptake progressively increased as the surface acidity decreased, and the oxidized sample heat-treated at 950°C had the same adsorption capacity as the as-received one, despite the lower surface area of the former sample compared with the latter. 

Specific Surface Areas of Different Carbons from Phenol Adsorption Isotherms and BET Plots... 

Cost estimation and screening external MSAs To determine which external MSA should be used to remove this load, it is necessary to determine the supply and target compositions as well as unit cost data for each MSA. Towards this end, one ought to consider the various processes undergone by each MSA. For instance, activated carbon, S3, has an equilibrium relation (adsorption isotherm) for adsorbing phenol that is linear up to a lean-phase mass fraction of 0.11, after which activated carbon is quickly saturated and the adsorption isotherm levels off. Hence, JC3 is taken as 0.11. It is also necessary to check the thermodynamic feasibility of this composition. Equation (3.5a) can be used to calculate the corresponding... 

Thus, log-log plots of S versus C provide an easy way to obtain the values for K (the intercept) and N (the slope of the line). The log-log plot can be used for graphic interpolation of adsorption at other concentrations, or, when values for K and N have been obtained, the amount of adsorption can be calculated from Equation 20.9. Figure 20.9 shows an example of adsorption isotherms for phenol adsorbed on Frio sandstone at two different temperatures. Note that when N = 1, Equation 20.9 simplifies to Equation 20.6 (i.e., adsorption is linear). 

The basicity of OLOA 1200 has been evidenced by its interaction with the oil-soluble acidic indicator dye, Brom Phenol Magenta E (EK 6810) which is normally yellow but turns blue and then magenta with increasing bacicity. The acidic form has an adsorption peak at 390 nm, the basic at 610 nm, and the isobestic point is at 460 nm. These spectra have be used to determine the concentration of OLOA 1200 in solution for adsorption isotherms. 

In Eqs. 31J and 32J we used Ihe same value of the size parameter n. This assumption may not be generally correct, since the species being adsorbed are not identical. Even if they do not differ in actual size (the removal of one proton does not change the size of a phenol molecule significantly), their orientation on the surface could be quite different, and the number of water molecules replaced may not be the same. This is not relevant to the derivation of the combined adsorption isotherm, since we are dealing with the process shown in Eq.32J only. 

The synthesis of phenolic-formaldehyde and melamine-formaldehyde resins in the presence of fumed silica allows obtaining porous organic materials with a differentiated porous structure and surface properties. The pore characteristics of the studied resins in dry state were determined from nitrogen adsorption isotherms. The differences in surface character of the synthesized polymers were estimated satisfactorily by XPS spectra showing the presence of various functional groups. The adsorption/desorption mechanism of water and benzene on the investigated porous polymers was different due to differentiated hydrophobicity of the bulk material. 

The membrane developed in this work and a cottunercial activated carbon F-400 (Calgon), which is widely used in various water treatments, were used for adsorption experiments. The adsorption isotherms of phenol were measured according to the following batch adsorption method. The sealed vial was placed in a constant-temperature water bath kept at 25 T . The samples were well stirred, using a magnetic stirrer overnight (Sakoda et al, 1991). 

The adsorption capacity of the activated carbon membrane for thus particular adsorbate was similar to that of F-400, suggesting the possibility that the adsorption capacity is increased by somehow developing larger micropores within the carbonized microspheres. In spite of their different compounds of polymer latex. Membranes A and B had almost the same amounts of adsorption. Figure 3 Adsorption isotherms of phenol... 

FIG. 18 Effect ol pH on the adsorption isotherms of phenol on polarized carbon Hbers. (Adapted from Ref. 420.)... 

We shall refer to this as the n n interaction argument. It has been formulated ba,sed on the following experiments (1) adsorption isotherms of phenol, nitrobenzene, and sodium benzenesulfonate on a series of activated carbons and carbon blacks and (2) characterization of the surface chemistry of as-received and chemically modified carbons. The authors did not report the pH in fact, this word is not even mentioned in any of their papers on this subject [450,331,332]. 

Multiple Adsorbates Adsorption isotherms are defined for individual adsorbate species. Collective parameters like DOC, phenols, and humic acids can only be used empirically as adsorbate parameters. Adsorption isotherms with collective parameters cannot be used for simple mechanistic interpretation of the data, even if these data can be fitted to such equations (Tomaic and Zutic, 1988). 

Figures 4.26A and 4.26B compare the results of the experimental determination of isotherms using the traditional mass balance method (MMB) and those obtained with MMC. The adsorption isotherm predicted by MMC deviates significantly from the isotherm data obtained by MMB. This may be due to the limited applicability of the Langmuir competitive model for the modeling of the adsorption behavior even of such simple systems as p-cresol and phenol in reversed-phase chromatography. Figures 4.26C and 4.26D compare the results obtained by MMB and HMMB for the same system. Over most of the concentration range, the agreement between the experimental data and the results of these two methods is...

Figure 4.26 Comparison of the competitive adsorption isotherm measured by FA and calculated by two different methods. p-Cresol (Left) and phenol (Right), Top Data from the mass balance method (MMB, binary frontal analysis) at molar ratios of 3 1 (Q)/ Id ( ) and 1 3 (A). Solid hnes calculated by the method of composition velocity (MMC). Bottom Comparison of the competitive isotherms obtained by MMB (Q) and HBBM (square s)nnbol) (n) for p-ciesol and phenol in three concentration regimes. Reproduced with permission from J. Jacobson and J. Frenz, ]. Chromatogr., 499 (1990) 5 (Figs. 2 and 5).

Figure 13.3 Adsorption isotherms of resorcinol, catechol, and phenol on Lichrosorb RP-18 measured by FA and by system peak analysis. Reproduced with permission from S. Levin, S. Abu-Laji, S. Golshan-Shirazi, G. Guiochon, J. Chro-matogr. A, 679 (1994) 213 (Fig. 3).

Levin et al. [22] measured by FA the single-component adsorption isotherms of resorcinol, catechol, and phenol on a Lichrosorb RP-18 column from aqueous solutions. They also determined these isotherms by integration of the retention factor, fc, of the system peak versus the additive concentration, C (see Eq. 13.23). A comparison of the two sets of results is shown in Figure 13.3. It shows a good agreement between the two sets of isotherms. 

It has long been known [16], and has more recently been confirmed by many authors [1], that phenol adsorption presents certain complexities, such as the occurrence of two distinct plateaus in the isotherm. In addition, the phenol uptake decreases upon oxidation of the activated carbons. 

More recently, Terzyk [32] also suggested that the irreversibility of phenol adsorption is due to the creation of strong complexes between phenol and surface carbonyl and lactone groups and to phenol polymerization. Salame and Bandosz [33] studied phenol adsorption at 30 and 60°C on oxidized and nonoxidized activated carbons. They concluded, from analyses of the isotherms by the FreundUch equation and the surface acidity of the carbons, that phenol was physisorbed by tt—tt dispersion interactions, whereas it was chemisorbed via ester formation between the OH group of phenol and surface carboxyl groups. 

Hamdaoui, O. and Naffrehoux. E.. Modeling of adsorption isotherms of phenol and chlorophenols onto granulai- activated carbon. Part I. Two-parameter models and equations allowing determination of thermodynamic parameters, J. Hazardous Mater., 147, 381, 2007. 

It was found, however, that hypercrosslinked sorbents exhibit much higher adsorption capacities. Fig. 11.7 illustrates sorption isotherms for phenol on the biporous sorbents MN-200 and MN-150. The isotherms coincide completely, thus revealing no difference in the phenol adsorption between the two neutral resins that only differ in the size of their macropores [53]. Both MN-200 and MN-150 absorb about 0.4g of phenol per gram of polymer without yet achieving fuU saturation of the resins. This value practically coincides with the amount ofsweUing water that is taken up by the hypercrosslinked polymeric phase of the biporous network. 

Two researches studied the adsorptive properties of montmorillonite clay modified by tetra-butyl ammonium (Akgay, 2004, 2005). The adsorption of p-chlorophenol in this clay was done in batch with 20 mL of pollutant solution to 0.1 g of clay, at 25°C for 16 h. The adsorption isotherms were adjusted according to the models of Freundlich and Dubinin-Radushkevich. The kinetic and thermodynamic parameters pointed to the application of organoclay as adsorbent effective of phenolic compounds in contaminated effluents. 

Other research confirmed the influence of the modification of bentonite in their adsorptive properties. The adsorption isotherms were determined with solutions of phenol in concentrations 50 mg L-i to 1000 mg L L in pH 6.5, at 20°C and 24 h. Structural changes were carried out with tetra-decy 1-trimethyl-ammonium bromide (TDTAB) and hexa-decyl-trimethy 1-ammonium bromide (HDTAB), with changes in 25%, 50% and 100% of capacity exchange cation. The equilibrium time was approximately 7 h and kinetic results indicated the possible presence of heterogeneous regions on the surfaces of clays modified with 25% and 50% of its cation exchange capacity. The clays modified with TDTAB and HDTAB in 100% obtained the best results for the removal efficiencies (Yilmaz Yapar, 2004). 

Barros Junior, L. M. (2004). Removal of Phenol in Wastewater Oil Refineries. Reoista Petroqmmica, Petrdleo, Gas Qutmica, vol. 266, p>p. 58-62. ISSN 0329-5001. Benmaamar, Z. Bengueddach, A. (2007). Correlation with different models for adsorption isotherms of m-xylene and touene on zeolites. Journal of Applied Sciences in Emriromental Sanitation, vol. 2, pp. 43-53. ISSN 0126-2807. 

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