Activated carbon adsorption of phenols

Knettig, E., Thomson, B.M., and Hrudey, S.E. Competitive activated carbon adsorption of phenolic componnds, Environ. PoIIut (SeriesB), 12(4) 281-299, 1986. 

Tessmer, C.H., Vidic, R.D., and Uranowski, L.J., Impact of oxygen-containing surface functional groups on activated carbon adsorption of phenols. Environ. Sci. Technol., 31, 1872, 1997. 

Problems Faced in Activated Carbon Adsorption of Phenols—Oligomerization.438... 

Nakhla, G., N. Abuzaid, and S. Farooq. 1994. Activated carbon adsorption of phenolics in oxic systems effect of Ph and temperature-variations. Water Environment Research 66(6) 842-850. 

Activated carbon has high specific surface area with respect to its volume, and thus has high adsorption capacity. Activated carbon adsorption is considered to be one of the most versatile treatment technologies and can remove classical pollutants such as COD, TOC, BOD, and nitrogen, as well as toxic pollutants such as phenol, refractory organic compounds, VOCs, and soluble heavy metals.38 Activated alumina and peat have also demonstrated similar abilities. 

More recently, Kander and Paulaitis (16) have studied the adsorption of phenol onto activated carbon and measured its sorption equilibria from dense C02. These researchers found that temperature controlled the adsorption equilibria and that phenol uptake was negligibly effected by changes in the gas phase density. Such a result indicates that factors other then a solute s solubility in a dense gas play a key role in defining the adsorption equilibrium which accompany such processes. 

The important role of electrostatic interactions is clearly seen in the study of Moreno-Castilla et al. [69] which dealt with the adsorption of substituted phenols (whose pKa ranged from 7.13 for /j-nitrophenol to 10.17 for p-cresol) on a series of well characterized activated carbons, all of which exhibited the expected decrease in uptake at high pH values. Table 27 summarizes the key results. Sample CP-10, with the highest surface area and the most developed porosity, had the highest adsorption capacity for all phenols. However, the pH at which the adsorp-... 

TABLE 27 Adsorption of Phenol and Substituted Phenols on Two Coal-Derived Activated Carbons... 

Liu X, Pinto NG. Modeling the Adsorption of Phenol and Aniline on Active Carbon. 23rd Biennial Conference on Carbon. State College, PA American Carbon Society, 1997. 

The secondary effluent from a biological treatment plant is treated with the activated carbon adsorption process and allowed to arrive at eqnilibrinm. The equilibrium data in terms of phenol are given below. Determine the constants for the Langmuir and Freundlich isotherms. 

Arafat et al. [4] studied the effect of the concentration of inorganic electrolyte on adsorption of benzene, toluene and phenol from aqueous solution at pH 11.6 on one commercial and two modified activated carbons and obtained very different results for these three adsorbates. The uptake of benzene was rather insensitive to the ionic strength. The uptake of toluene systematically decreased when the ionic strength increased. Finally the uptake of phenol was enhanced on addition of 0.5 mol dm KCl, but further addition of salt depressed the uptake and with 0.8 mol dm"" KCl the uptake dropped below that observed at low ionic strength. Adsorption of phenol on activated carbons was recently studied by other research groups [12,13], but without emphasis on the possible effects of pH dependent surface charging. 

Fernandez, E., Hugi-Cleari, D., Lopez-Ramon, M.V., et al. (2003). Adsorption of phenol from dilute and concentrated aqueous solutions by activated carbons. Langmuir, 19, 9719-23. 

Magne, P. and Walker, P.L., Jr (1986). Phenol adsorption on activated carbons application to the regeneration of activated carbons polluted with phenol. Carbon, 24, 101-7. 

Stoeckli, F., L6pez-Ram6n, M.V., and Moreno-Castilla, C. (2001). The adsorption of phenolic compounds from aqueous solutions by activated carbons described by the Dubinin—Astakhov equation. Langmuir, 17, 3301-6. 

The foregoing interpretation, however, gives no clue to explain the pattern of phenol adsorption as disclosed in the same experiment. During the initial activation, adsorption of phenol increased gradually to 0.15 gjg carbon when the surface area had reached 600 sqm/g but beyond this point any further enlargement of the surface made no further increase in the amount of phenol adsorbed. From this we might conclude that all surface created above 600 sq m/g carbon had no adsorptive power for phenol. 

Adsorption of SOC by activated carbon may involve various combinations of chemical, electrostatic, and physical (i.e. non-specific dispersion forces) interactions [59]. The overall adsorption interactions can be very complex for some SOCs. One good example is the adsorption of phenolic compounds, probably the most widely studied class of adsorbates in the activated carbon literature. Several possible mechanisms have been proposed for phenol adsorption [60-69]. These incluile (i) n-n dispersion interactions between the basal plane of activated carbon and the aromatic ring of the adsorbate, (ii) electrostatic attraction-repulsion interactions, (iii) hydrogen bonding between adsorbate and surface functional groups of activated carbons, (iv) electron acceptor-donor complex formation mechanisms between the carbonyl... 

For the adsorption of micro-organics (p-nitrophenol, benzoic acid) in fixed-bed columns, the half breakthrough time increases proportionally with increasing bed depth but decreases inversely proportionally with increasing water flow rate [54,55]. By studying the adsorption of chloroethylenes on activated carhon fibers, Sakoda et al. [56] determined a linear relationship between the overall mass transfer coefficient (Kfu) and the flow rate Uo. The influence of temperature on file dynamic adsorption of phenol on fibrous activated carbon has also been demonstrated [57]. 

Teng, H. To, C. (2000). Liquid-phase adsorption of phenol onto activated Carbons Prepared with Different Activation Levels. Journal of Colloid Interface Science, vol. 230, pp. 171-175. ISSN 0021-9797. 

Adsorption of phenol and its derivatives from aqueous solutions on active carbons and carbon blacks has been the subject matter of a large number of investigations. Jaroniec and coworkers,Enrique et al. Worch and Zakke, and Magne and Walker studied the adsorption of several phenols from aqueous solutions and found that the adsorption was partly physical and partly chemical in character. Aytekin, ChapUn, and Kiselev and Krasilinkov observed that the adsorption isotherms of phenol from aqueous solutions were step-wise, suggesting the possibility of rearrangement of phenol molecules in the adsorbed phase and their interaction with active sites on the carbon surface. Morris and Weber, however, found that the adsorption isotherms of phenols on active carbons show two plateaus, even... 

Abuzaid and Nakhla, and Vidic et al. found that the adsorption of phenol by activated carbons from aqueous solutions in the presence of molecular oxygen in the test environment resulted in a threefold increase in the adsorption capacity of the carbon. This has been attributed to the oxygen induced polymerization reactions on the surface of the carbon. Juang et al. studied liquid-phase adsorption of eight phenohc compounds on a PAN-based activated carbon Fiber in the concentration range of 40 to 500 mg/L and observed that the chlorinated phenols showed better adsorption than methyl substituted phenols. Moreno-CastiUa et al. studied the adsorption of several phenols from aqueous solutions on activated carbons prepared from original and deminerahzed bituminous coal and found that the adsorption capacity depended upon the surface area and the porosity of the carbon, the solubility of the phenolic compound, and the hydrophobicity of the substituent. The adsorption was attributed to the electron donor-acceptor complexes formed between the basic sites on the surface of the carbon and the aromatic ring of the phenol. 

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